The nl_langinfo() and nl_langinfo_l() functions provide access to
locale information in a more flexible way than localeconv(3).
nl_langinfo() returns a string which is the value corresponding to
item in the program's current global locale. nl_langinfo() returns a
string which is the value corresponding to item for the locale
identified by the locale object locale, which was previously created
by newlocale(1). Individual and additional elements of the locale
categories can be queried.
Examples for the locale elements that can be specified in item using
the constants defined in <langinfo.h> are:
CODESET (LC_CTYPE)
Return a string with the name of the character encoding used
in the selected locale, such as "UTF-8", "ISO-8859-1", or
"ANSI_X3.4-1968" (better known as US-ASCII). This is the same
string that you get with "locale charmap". For a list of
character encoding names, try "locale -m", cf. locale(1).
D_T_FMT (LC_TIME)
Return a string that can be used as a format string for
strftime(3) to represent time and date in a locale-specific
way.
D_FMT (LC_TIME)
Return a string that can be used as a format string for
strftime(3) to represent a date in a locale-specific way.
T_FMT (LC_TIME)
Return a string that can be used as a format string for
strftime(3) to represent a time in a locale-specific way.
DAY_{1–7} (LC_TIME)
Return name of the n-th day of the week. [Warning: this
follows the US convention DAY_1 = Sunday, not the
international convention (ISO 8601) that Monday is the first
day of the week.]
ABDAY_{1–7} (LC_TIME)
Return abbreviated name of the n-th day of the week.
MON_{1–12} (LC_TIME)
Return name of the n-th month.
ABMON_{1–12} (LC_TIME)
Return abbreviated name of the n-th month.
RADIXCHAR (LC_NUMERIC)
Return radix character (decimal dot, decimal comma, etc.).
THOUSEP (LC_NUMERIC)
Return separator character for thousands (groups of three
digits).
YESEXPR (LC_MESSAGES)
Return a regular expression that can be used with the regex(3)
function to recognize a positive response to a yes/no
question.
NOEXPR (LC_MESSAGES)
Return a regular expression that can be used with the regex(3)
function to recognize a negative response to a yes/no
question.
CRNCYSTR (LC_MONETARY)
Return the currency symbol, preceded by "-" if the symbol
should appear before the value, "+" if the symbol should
appear after the value, or "." if the symbol should replace
the radix character.
The above list covers just some examples of items that can be
requested. For a more detailed list, consult The GNU C LibraryReference Manual.

On success, these functions return a pointer to a string which is the
value corresponding to item in the specified locale.
If no locale has been selected by setlocale(3) for the appropriate
category, nl_langinfo() return a pointer to the corresponding string
in the "C" locale. The same is true of nl_langinfo_l() if locale
specifies a locale where langinfo data is not defined.
If item is not valid, a pointer to an empty string is returned.
The pointer returned by these functions may point to static data that
may be overwritten, or the pointer itself may be invalidated, by a
subsequent call to nl_langinfo(), nl_langinfo_l(), or setlocale(3).
The same statements apply to nl_langinfo_l() if the locale object
referred to by locale is freed or modified by freelocale(3) or
newlocale(3).
POSIX specifies that the application may not modify the string
returned by these functions.

The following program sets the character type and the numeric locale
according to the environment and queries the terminal character set
and the radix character.
#include <langinfo.h>
#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
setlocale(LC_CTYPE, "");
setlocale(LC_NUMERIC, "");
printf("%s\n", nl_langinfo(CODESET));
printf("%s\n", nl_langinfo(RADIXCHAR));
exit(EXIT_SUCCESS);
}

This page is part of release 4.13 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2017-09-15 NL_LANGINFO(3)